Art of cracking petroleum oils



Nov. 1, 1938. P. OSTERGAARD 2,135,109

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Patented Nov. 1, 1938 PATENT OFFICE ART OF CRACKING PETROLEIM OILS Povl Ostergaard, Mount Lebanon, 'Pa.,' assignor to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application December 2, 1936, Serial No. 113,906

8 Claims.

This invention relates to the art of crackin petroleum oils and it comprises a process 'of making motor fuel or gasoline of high anti-knock value from hydrocarbon oil as well as normally gaseous hydrocarbons, such as those produced in cracking hydrocarbon oils, and such as natural gases and the like.

In my copending applications, Serial No. 52,717, filed December 3, 1935, and Serial No.

97,295, filed August 21, 1936, of which applications this application is in part a continuation. I disclosed a process of cracking hydrocarbon oil, such as naphtha or relatively heavy oil, wherein the oil is subjected to thermal conversion in the presence of normally gaseous hydrocarbons containing 3 to 4 carbon atoms per mole-.-

disclosed in my application Serial No. 97,295, the

operation is so conducted that the hydrocarbon oil is subjected'to a higher degree of conversion per pass, in the presence of the normally gaseous hydrocarbons, than can be attained in similar apparatus when cracking the same oil aloneand without the presence of the normally gaseous hydrocarbons. Under such conditions the degree of conversion per pass, or the crack per pass, may be increased over that which could be. obtained under practical conditions in the conversion of the oil alone. The resultant gasoline procluct represents a material of extremely high anti-knock value, the major portion of the increase in anti-knock value obtained resulting from the increased conversion of the oil and the balance of the increase in octane 45 number of the gasoline being due to polymerization of gas constituents and inter-reaction between gas constituents and the oils or products of conversion thereof.

The specific processes described and illustrated in the above-mentioned copending applications are of the single coil type and are preferably, although not necessarily, of the ence-through type, i. e. they are operations whichare preferably conducted without recycling oil to the conversion coil.

I have found that whereas straight-run gas oils can be cracked by themselves to between 15 to 30 per cent crack per pass, the same gas oils diluted with normally gaseous hydrocarbons containing 3 to 4 carbon atoms per molecule can be cracked in similar apparatus to from to 60 per cent conversion per pass. Similarly, whereas a residual petroleum oil such as a reduced crude may be cracked by itself to from 5 to 12 per cent crack per pass, the same oil, diluted with liquefied normally gaseous hydrocarbons containing 3 and 4 carbon atoms per molecule may be cracked to from 10 to 25 per cent conversion per pass. Similarly, naphthas with boiling ranges lying'between approximately 200 and 500 F. may be cracked toa higher degree of conversion per pass in the presence of liquefied normally gaseous hydrocarbons containing 3 and 4 carbon atoms per molecule than when cracked alone. In each instance, while the gasoline-like polymers resulting from the straight polymerization of the normally gaseous hydrocarbons are included in figuring the degree of conversion per pass or the degree of crack per pass, the ultimate conversion per pass'or crack per pass is in excess of that obtained by simply considering the normal production of gasoline from the oil alone and the normal production of polymers from the normally gaseous hydrocarbons alone, when these oils and normally gaseous hydrocarbons are separately subjected to conversion; the results are betterthan the sum of the results obtained by separately cracking the oil and polymerizing the gases.

Moreover, the production of tar is materially reduced; due probably to the fact that nascent products of conversion of the hydrocarbon oil, which would otherwise undergo polymerization to form tan-react with saturated or unsaturated gaseous. compounds to a much greater extent than is truewhen oil is cracked alone and in the absence of added normally gaseoushydrocarbons, The products of such reaction tend to be rich in aromatics and havelower molecular weights and lower boiling points than the oils which would be formed by a combination of In the process disclosed in the present application, I have applied the general teachings and plrinciples of the inventions disclosedin the aforementioned copending applications to the cracking of hydrocarbon oil in a so-called combination unit of the multi-coil type, with advantageous results. In such a unit, the starting material is usually a crude petroleum oil. The

crude oil is first stripped to recover segregated fractions of definite boiling-point ranges as well as a stripped or reduced crude, and a number or all of the segregated fractions are cracked under optimum conditions for their conversion, the hot cracked products thus obtained being combined in such manner as to simplify recovery of the products and segregation of the various charging and recycle stocks. Where desired,- the topped or reduced crude may be subjected to a mild cracking or so-called viscosity-breaking operation for the purpose of producing a clean charging stock for subsequent cracking of gasoline rather than for the production of a high yield of gasoline directly by cracking the reduced crude under more severe conditions.

In one specific type of operation described in detail hereinbelow and especially applicable to crude petroleum of relatively low sulfur content,

the crude is heated, preferably by heat exchange in the system, and discharged into an atmospheric stripping tower where light gasoline boiling up to about 200 F., naphtha boiling from 200 to 400 or 500 F. and, if desired, kerosene, are removed andrecovered. The'stripped petroleum is then charged into the upper portion of a separating tower receiving hot cracked products from a number: of cracking operations, and by direct heat exchange with these hot cracked products is further reduced. The reduced crude, commingled with normally gaseous hydrocarbons, iscracked in a suitable coil and the hot cracked products are discharged into the lowerportion of said separating tower.

from the separating tower-are fractionated to I remove gas-oil constituents boiling between about 300 and 700 F. and are then introduced into a condensing and stabilizing system for the eventual recovery of stabilized gasoline, having an :The vapors and gases leaving the condensing and stabilizing system are further condensed to provide a liquid fraction consisting largely of hydrocarbons having 4 carbon atoms per molecule, this liquid fraction. being commingled at least in part with the reduced crude about to be cracked. The naphtha recovered in the crude stripping tower is used as an absorbentto remove the higher boiling constituents of the gases remaining after the aforesaid condensation, and the thereby enriched naphtha is reformed in a separate heating coil, the hot reformed products being delivered to the lower portion of the separating tower. The gas-oil recovered as described hereinabove is employed as an absorbing medium in a second absorber which may receive gases from an extraneous source, or gases leaving the first-mentioned absorber, or both, and the thereby enriched gas-oil containing Y dissolved. hydrocarbons having 3 to 4 carbon atoms per molecule is d elivered to a third cracking coil, the

hot cracked products therefrom passing to the separating tower along with the hot cracked The vapors tail hereinbelow, the crude charging stock is first distilled in a. crude stripping tower, light gasoline, naphtha and gas-oil fractions being recovered from this tower. The reduced crude is subjected to a mild cracking or viscosity-breaking operation and the hot viscosity-broken products are discharged back into a-lower portion of the crude stripping tower, tar being separated and the vapors passing into the upper portion of the crulie stripping tower for recovery and fractionation along with the initially heated crude 011.

The naphtha and. gas-oil fractions thus recovered, after passing through separate absorbers wherein they are enriched with normally gaseous hydrocarbons, are reformed and cracked, respectively, in separate coils, and the cracked products, after quenching, are delivered to a separator from which tar and vapors are separately removed. The vapors are fractionally condensed to remove gas-oil, stabilized gasoline and a liquid butane fraction. The gas-oil and the butane fraction are combined and delivered to a sepa: rate recycling coil from which the hot cracked products pass into the separator along with the products from the reforming coil and the virgin gas-oil cracking coil. The, remaining gases and vapors pass through the naphtha absorber and either resultant scrubbed gases or gases from an extraneous source, or both, then pass through the gas-oil absorber. This-type of operation is especially suitable for crude petroleum stocks of relatively high sulfur content.

r In a third type of operation also described in detail hereinbelow and especially adapted to the treatment of crude oil from which it is desired to recover lubricating oil constituents, the crude oil is first topped to recover light virgin gasoline, heavy naphtha and gas-oil fractions, the topped crude being withdrawn from the system and substantially treated for the recovery of the lubricating oil constituents contained therein. The heavy naphtha and gas-oil fractions thereby recovered are used as absorption media in separate absorbers for the recovery of normally gaseous hydro carbons from mixed hydrocarbon gases produced ashereinafter set forth, and the enriched fractions are then subjected .to reforming'and cracking, respectively, in separate coils. The hot cracked products from these coils are then discharged together into a vapor-separator from which tar is removed. Thevapors are fractionated to recover gas-oil cycle stock and. stabilized gasoline. The remaining gases and'vapors are passed to the absorption system. The gas-oil cycle stock is recycled to a separate coil, preferably in admixture with hydrocarbons having 3 'to fcarbon atoms per molecule obtained by subjecting the cracked gases to condensation between the gasoline condensation stage and the absorption stage. The hot cracked products from the recycling coil are also delivered to the vapor separator, together with the products from the reforming and cracking coils.

It is a characteristic of my process described herein, in certain of its embodiments,'that the virgin or uncracked stocks are largely or wholly subjected to conversion in a once-through manner, that is to say, without recycling, whereas cracked gas oil constituents from the various operations are largely or wholly segregated and subjected to conversion in a-recirculatory or cyclic manner; in short, recycling operations are primarily confined toa single coil, which coil receives only previously cracked products. In the case of each stock, the conversion is, however, conducted purposes of this invention as though it were a virgin or uncracked stock, that is to say, it is cracked, either alone or with strictly virgin gas: oil, in a once-through manner, while such products of the more drastic cracking'as fall within the gas-oil boiling-point range are recycled to a separate coil. I have found that this principle of operation, particularly in conjunction with the recycling of normally'gaseous hydrocarbons and the regulation of the gas-recycle ratios, makes it possible to obtain better results than can be obtained when operating a combination unit without benefit of my invention.

Important objects achieved in the utilization of my invention are the production of a high yield of gasoline of high anti-knock value when used as a motor fuel, reduction in the amount of tar produced, thermal economy, and the utilization to the best advantage of the gases produced in the operation.

My invention has for further objects, however,

such additional operative advantages and improvements as may hereinafter be found to obtain.

In order that my invention may be fully set forth and understood, I now describe, with reference to the drawings accompanying and forming part of this specification, various preferred forms and manners in which my invention may be practiced and embodied. In these drawings,

'Figures 1A, 1B and 1C are vertical elevational views of various portions of an assembly of apparatus adapted for the performance of the process of my invention; the apparatus being shown in more or less diagrammatic form. In examining the drawings and applying the descriptive matter of the specification thereto, Figures 1A, 1B and 1C are intended to be placed side by side in the order indicated, reading from left to right; when thus arranged these figures form a single figure illustrating the entire apparatus assembly used in the process;

Figs. 2A, 2B and 2C are similar views of various portions of an alternative form of apparatus adapted for the performance of the process of my invention in a somewhat different embodiment;

and

Figs. 3A and 3B are type of apparatus for carrying out the process of my invention in a still further embodiment thereof.

Similar reference numerals designate similar parts in all the several views of the drawings.

Referring now to the drawings, and more particularly to Figs. 1A, 1B and 10 thereof, the

principal apparatus elements consist of a furnace I provided with several sets of cracking coils to be described hereinbelow, a separating tower 2, a fractionating tower 3, a crude stripping tower 4, a vapor-feed condenser and stabilizer 5, absorbers 6 and I and a tar flasher 8, together with various pipes, separators, accumulators, pumps. valves, heat exchangers and other incidental equipment. The function and purpose of the various units will be made moreclear from the description set forth hereinbelow.

similar views of a further Crude petroleumoil is introduced into the system through a line l and is forced by a pump I I through a line l2, a heat exchanger l3, a line l4, a heat exchanger l5 and a line l6 into the atmospheric-pressure crude stripping tower 4 at an intermediate level therein. The crude stripping tower 4, which receives the crude oil preheated in the heat exchangers l3 and i5, is provided with conventional plates or trays I1 and may also be provided as shown with an entrainment separator 18 at the point of introductionof the heated oil thereto.

In the crude stripping tower 4 the crude oil, which has been heated to an elevated temperature of from 300 to 700 F., preferably about 500 F., in heat exchangers l3 and I5, is partially vaporized and the vaporized portions are subjected to fractional condensation and recti fication. In order'to assist in the condensing and rectifying action some cooling is necessary. This cooling may be provided by locating an indirect heat exchanger or cooling coil in the upper part of the crude stripping tower 4 or by supplying to the top of the crude stripping tower 4 a cool liquid reflux medium. In a preferred instance shown, a side stream is withdrawn from a point near the top of the tower 4 through a line l9, this side stream passing to a cooler 20 and then being returned by means of a pump 2 l and a line 22 to the top of the stripping tower 4 to serve as a cooling and refluxing medium therefor. It will be obvious to those skilled in the art that while the particular form of cooling and refluxing means disclosed is preferred, various other expedients may be employed for the purpose of providing the necessary cooling andrefluxing in the tower 4.

The lowest boiling constituents, consisting of light virgingasoline, pass uncondensed from the top of the crude stripping tower 4 through a line 23 to a cooler or condenser 24 and thence to a separator 25 having a vent 26. The condensate collecting in the separator 25 may be withdrawn therefrom through a line 21 and removed from the system, or it may be used in whole or in part as a refluxing and condensing medium elsewhere in the system.

A naphtha side stream, consisting of somewhat higher boiling condensed naphtha constituents, having a boiling range of for example from 200 to 500 F., is withdrawn from the upper portion of the tower 4 through a line 28, while a still heavier side stream consisting primarily of kerosene or furnace oil constituents is withdrawn from the tower 4 through a line 29 and delivered to a kerosene stripper. 30. Vapors removed in the stripper 30 are returned to the tower 4 through a vapor-return line 3|, while the stripped kerosene or furnace oil is withdrawn from the stripper 30 through a line 32, passing through a cooler 33 on its way out of the system.

The remaining portion of the partially distilled crude, which will henceforth be referred to as stripped crude, is removed from the bottom of the stripping tower 4 through a line 35 and passes to an accumulator 36, which is provided with a vapor line 31 leading back into the stripping tower 4. It will be understood that in this instance the virgin gas-oil constituents present in the original crude remain largely in the stripped crude.

The stripped crude from the accumulator 36 is then delivered through a line 38, a pump 39 and a line 40 to the upper portion of the separating tower 2. The separating tower 2 is proa further distillation of the stripped crude delivered through the line 40. The fractionation is assisted by means of reflux supplied to the top of the tower 2 through a line 44 The reducedcrude accumulating on the tray 4| is withdrawn therefrom through a line 45,

wherein is located a pump 48, and is then admixed with liquefied normally gaseous hydrocarbons, primarily butane and butylene, introduced to the line 45 through a line 41 from a source to be described hereinbelow. The mixture of reduced crude and liquefied normally gaseous hydrocarbons then passes through a heated coil 48 located within the furnace I. The coil 48 advantageously consists of an initial heating section having a high heat input, and a soaking section with a lower heat input. The percentage by volume of the liquefied gaseous hydrocarbons will ordinarily amount to between 10 and |00 per cent of the reduced crude.

In the heating coil 48 the mixture of reduced crude and normally gaseous hydrocarbons is subjected to conversion at a temperature of from 800 to 1000 F. and under a pressure varying between 100 and 1000 pounds per square inch,

the conditions being such that the degree of conversion per pass or crack per pass obtained is higher than could be obtained in the same apparatus if the reduced crude were charged through in the absence of added normally gaseous hydrocarbons. In a typical instance the operating conditions may be such as to give a coil-outlet temperature of about 925 F. and a coil-outlet pressure of about 750 pounds per square inch, the ratio of volume of liquefied gas to the liquid volume of the reduced crude under atmospheric'conditions being approximately 1:3 and the reduced crude being. one which could not well be subjected to a coil-outlet temperature of more than about 875 F. in the same coil in the absence of the added normally gaseous hydrocarbons.

In the heating coil 48 the reduced crude and such heavy recycle oil as may have been accumulated therewith in the separating tower 2 is cracked in the presence of the normally gaseous hydrocarbons; the degree of conversion per pass being from 10 to 25 per cart. The gases themselves manifest some tendency to crack" and polymerize and to combine with products obtained in cracking the heavy oil, the tendency being to form a greater percentage of hydrocarbons' boiling below 700" F. and a smaller percentage-of hydrocarbons boiling above 700 F.

than would be the case if the heavy oil were cracked by itself. The reactions which take place are involved and complex but actual experiments in commercial scale operationhave proved that these reactions do take place.

The hot cracked products from the coil 48 then pass through a transfer line 49 and a pressure reducing valve 50 into the lower portion of the separating tower}, where they separate into vaporou's and liquid products. The vapors pass upward into the upper portion of the separating tower as aforesaid while the separated liquid or tar is withdrawn through a line 5|. A portion 01' the tar may be returned through a line 52, a cooler 53, a pump 54 and a. line 55 to the bottom of the separating tower 2 in order to minimize or prevent the formation of coke therein while the remaining portion passes through a. line 56 and a valve 51 into the tar flasher 8, the interior of which is provided with baiiles 58 and a suitable number of plates or trays 59. Flashed tar is withdrawn from the bottom of'the tar flasher 8 through a line while the liberated vapors pass through a line 6| to a cooler or condenser 62 and thence to a separator 63 having a gas vent 64. The condensate recovered in the separator 63 is advantageously returned by means of a line 65 and a pump 66 to the line 44, thus entering the upper portion of the separating tower 2 as a cooling and refluxing medium therefor.

The substantially tar-free vapors leaving the top of the separating tower 2 pass through a vapor line 10, the heat exchanger l5 and a line II to the lower portion of the main fractionating tower 3, the purpose of which is to remove constituents boiling above the boiling point range of the desired gasoline fraction subsequently to be condensed, i. e. to remove clean charging stock or gas oil constituents, including such products of reaction between gases and products of conversion of the oils as fall within the gas-oil range. For this purpose the fractionating tower 3 is provided with suitable cooling and refluxing means. In the instance shown this means comprises a side stream withdrawal line 73 which serves to withdraw a liquid side stream from a point near the top of the fractio'nator 3. This side stream then passes through a heat exchanger 14 and a cooler 15 and is then returned by means of a pump 16 and a line TI to the top .of the fractionator 3. Gasoline vapors and lighter constituents uncondensed in the fractionator 3 are withdrawn through a vapor line 18 while gas-oil condensate, having a boiling range of for example from 400 to 700 F., is withdrawn from the bottom of the fractionator 3 through a line 19.

The gasoline vapors and gases leaving the tower 3 through the line 18 pass to a vapor-feed condenser and stabilizer 5 which consists of a condensing section 80 and a stabilizing section 8| separated by a trap tray or weir device 82. The sections 80 and 8| are interiorly provided with suitable plates or trays 83. Unstabilized gasoline condensate is withdrawn from the tray 82 through a line 84 and passes through the heat exchanger 3 and a cooler 85, being then returned to the upper portion of the condensing section 80 by means of a pump 86 and a line 81, thus serving as a cooling and refluxing medium for the condensing operation. As shown in the drawings, the reflux so supplied may be supplemented by a portion of the light gasoline collected in the accumulator 25, this portion passing from the accumulator 25 through the line 21, a line 88, a pump 89, a line 90 and the line 81 into the condensing section 80 of the condenser and stabilizer 5.

The remaining portion of the unstabilized condensate passes downward into, the stabilizing section 8| where it is subjected to distillation and rectification for the purpose of removing undesirably light constituents. The vaporized constituents thereby liberated return in vapor form to the condensing section 80 while the thereby stabilized gasoline passes from the bottom of the stabilizer 8| through a' line 9| into a reboiler 92 the stabilizing section 8|. The stabilized gasoline leaving the reboiler 92 through a line 94 passes through a cooler 95 and thence through a line 96 having a valve 91 to storage. The valve 91 is preferably connected by means of operating mechanism-98 to a float or level device 99 attached to and forming part of the reboiler 92.

As will be clear from the above, the operation of the condenser and stabilizer is so conducted as to effect the recovery from the gases and vapors passing through the line 18 of stabilized gasoline ,hydrocarbon and fixed gases. The vapor-feed condenser and stabilizer is a highly advantageous feature of the apparatus illustrated, in that a vapor-feed condenser and stabilizer of this type is especially advantageous in the recovery of stabilized gasoline from vapors containing a high percentage of normally gaseous constituents and fixed gases. The operation and details of this condenser and stabilizer are further disclosed in my copending applications Serial No. 52,717, filed December 3, 1935, Serial No. 97,295, filed August 21, 1936, and Serial No. 103,947, filed October 3, 1936, the last mentioned application dealing primarily with the condenser and stabilizer itself, independent of a combined oil-cracking and gas-recycling unit, while the two earlier applications disclose the use of this vapor-feed condenser and stabilizer in conjunc tion with combined oil-cracking and gas-recycling units.

Thevapor-feed condenser and stabilizer 5 is advantageously operated, insofar as the present process is concerned, at a pressure of between 100 and 350 pounds per square inch, the preceding towers 3 and 2 being maintained under slightly higher pressures.

The vapors which leave the top of the condensing section 80 through a line IOI consist of low-boiling hydrocarbons ranging from methane on the one hand to butanes and butylenes on the other hand, and they may also contain some hydrogen. The hydrocarbons of lower molecular weight such as methane, ethane and ethylene are not sufiiciently reactive to warrant recycling them to the conversion units. Butanes and butylenes are, however, extremely reactive and it is desirable to recycle all of these constituents to the conversion units, as well as, to some extent at least, propane and propylene. I have found that it ordinarily does not pay commercially to return ethane and ethylene nor to try to efiect the recovery and recycling of all of the propane and propylene; it is desirable, however, to recover and return a considerable portion of the latter. In any event, the recovery and recycling of the normally gaseous hydrocarbons is so regulated as to avoid accumulation of these'gases in the system and to prevent the escape from the system of the butanes and butylenes.

A portion of the normally gaseous hydrocarbons, primarily butanes and butylenes, contained in the vapors passing through the line IOI may conveniently be recovered, under the operating pressures mentioned, by simply condensing the vapors. For the purpose I provide a cooler or condenser I02 located in the line IOI, and an accumulator or separator tank I03. A portion or all of the condensate thereby obtained may be delivered through a line I04, a branch line I05, a pump I06 and a line I01 to the heat exchanger I4 and thence through the line 41 to the inlet pipe 45 leading to the cracking coil 48, as described hereinabove.

The vapors separatedin the separator I03 pass through a line I08 into the lower portion of. the absorber 6. The remaining portion of the condensate from the separator I03 may also be delivered to the absorber 6 through a branch line I09 communicating with the pipe I04, having a pump H and terminating in the vapor line I08. This arrangement provides for a certain flexibility of operation, the condensate from the separator I 03 being divided between the lines I and I09 in such manner as to give proper recycle ratios in the various cracking coils.

In the absorber 6, the interior of which is provided with suitable plates or trays II I, the vapors and gases are scrubbed with a suitable hydrocarbon liquid absorption medium, preferably a low-Boiling oil such as naphtha, for the recovery therefrom of hydrocarbons containing 3 and 4 carbon atoms per molecule. In the preferred instance illustrated, the virgin naphtha removed as a side stream from the crude stripping tower 4 through the line 28 is advantageously employed as the absorption medium in the absorber 6.

This naphtha side stream passes through'the line 281 to a pump H2 and thence through a cooler H3 and a line II4 to the upper portion of the absorber 6. In descending through the absorber 6 the cooled naphtha thus introduced effects a selective absorption of the higher boiling components of the gases and vapors also traversing the absorber 6. At one or more points in the tower, as shown, suitable side streams may be withdrawn through lines H5 and II5a wherein are located pumps H6, II6a. and coolers I", la, respectively, and then returned to the absorber 6. This arrangement, which maybe repeated at convenient intervals throughout the length of the absorber 6, ,provides for the dissipation of the heat of absorption of the normally gaseous hydrocarbons in the liquid absorbing oil.

The enriched naphtha, containing dissolved normally gaseous hydrocarbons having 3 and 4 carbon atoms per molecule, leaves the bottom of the absorber 6 through a line I20 which communicates with an accumulator I2I having a. vapor return line I22 leading back into the absorber. 6. The enriched naphtha from the line I20 and the accumulator I2I then passes through a line I23, a pump I24, a line I25, a heat exchanger I26 and a line I21 into a preheating coil I28 located in the convection section of the furnace I and thence through a cracking coil I29 located in a hotter portion of the furnace I. The cracking coil I29 'is preferably composed of a heating section arranged for high heat input and a soaking coil arranged for a lower heat input.

As has been described in connection with the cracking coil 48, the mixture of oil and normally gaseous hydrocarbons traversing the coils I28 and I29 is subjected to cracking under conditions effective to give a higher degree of conversion per pass than could be obtained if the oil were separately passed through the same apparatus in the absence of the normally gaseous hydrocarbons. In general, sufficient heat will be supplied to give a coil-outlet temperature between 900 and 1450 F., the pressure varying between 300 and 3000 pounds per square inch. Typical oper- I More detailed operating conditions are fully disclosed in my copending application Serial No. 97,295 referred to hereinabove.

The hot cracked products leaving the coil I29 are first quenched by means of oil introduced through a line I30, to a temperature below an active conversion temperature, or at least to a temperature sufficient to prevent deposition of carbon in the transfer line, and then passed through a transfer line I3I having a pressurereducing valve I32, into the lower portion of the separating tower 2, the subsequent treatment of the separated vapors and liquid being as described hereinabove.

Where the gases leaving :the top of the absorber 6 still contain hydrocarbons having 3 or 4 carbon atoms per molecule, these gases are passed through a line I35 having a pressure regulating valve I36 and a cooler I3I, into a second absorber I, where they are subjected to further absorption. Hydrocarbon gases from an extraneous source, such as cracking plant gases, natural gas or other gases containing hydrocarbons of 3 and 4 carbon atoms per molecule may be introduced into the absorber I through a line I38 which terminates in the line I35 prior to the cooler I3I. Any condensate removed in the cooler I3I passes through a trap I39 into the lower part of absorber I In the absorber 1 the rising gases are subjected to a descending flow of a suitable absorbing oil for the purpose of recovering the higher boiling constituents of the gases, primarily hydrocarbons having 3 and 4 carbon atoms .per molecule. In the instance shown in the drawings the absorbent oil employed in the absorber I comprises gas-oil condensate recovered in the fractionator 3. This as-oil condensate is withdrawn from the bottom of the fractionator 3 through a line I9 and a por-- tion thereof passes through a line I 40, the reboiler 92, a line I4I, the heat exchanger I26, a line I42, a pump I43, a cooler I44 and a line I45 into the upper part of the absorber I, thence descending through the absorber I as an absorbing medium. It will be observed that with this method of operation the sensible heat of the hot gas-oil condensate is advantageously used to supply heat for reboiling in the stabilizer section 8I of the condenser and stabilizer and further heat exchange between this gas-oil and the enriched absorbent from the absorber 6 is also provided for.

The interior of the absorber I is conveniently provided with suitable plates or trays I46. In order to dissipate the heat of absorption of the normally gaseous hydrocarbons in the absorbent oil, a liquid side stream may be withdrawn at an intermediate point from the absorber I through a line I4I, this side stream being then delivered by means of a pump I48, a cooler I49 and a line I50 back into the absorber I. As in the case of absorber 6, this arrangement may be repeated at various levels in the absorber I. g

In passing into the absorber I the gas-oil picks up the higher boiling constituents of the hydrocarbon gases traversing the absorber. The enriched gas-oil then passes from the bottom of the absorber I through a line I5I into an accumulator I52 having a vapor-return line I53 leading back into the absorber I. The enriched gas oil accumulating in the accumulator I52 then passes through a line I54 having a pump I55 into a heat exchanger I56 and thence through a line I5I into a cracking coil I58 located in the furnace I. As described in connection with cracking coils 48 and I29, the cracking coil I58 advantageously comgases to the liquid volume of the recycle oil measured at atmospheric temperature will vary from 1:5 to 2:1, depending to some extent upon the quantity of extraneous gases introduced into the absorber I through the line I38. As described in connection with the cracking operations taking place in the coils 48 and I29, the cracking of the gas-oil and absorbed normally gaseous hydrocar-bons involves a cracking of the gas oil under conditions more drastic than could be obtained if the oils were cracked alone, cracking and polymerization to some extent of the normally gaseous hydrocarbons, and inter-reaction between normally gaseous hydrocarbons and the products of conversion of the oil undergoing cracking. The result is the production of a high yield of gasoline of high anti-knock value and a reduction in the amount of tar formed in the conversion operation, as compared with operations in which gas oil is cracked in the absence of normally gaseous hydrocarbons. The desired advantageous results are not, however, fully obtained unless the conditions of conversion are so regulated as to efiect a higher crack per pass of the gas oil than could be obtained in the same apparatus without .the presence of the normally gaseous hydrocarbons.

The hot cracked products leaving the outletof the coil I58 are then quenched by means of relatively cool oil introduced through a line I59 to a temperature below an active conversion temperature or at least to such extent as to prevent undesirable deposition of carbon in the transfer line and then passthrough a transfer line I60 having a pressure-reducing valve I6I into the lower portion of the separating tower 2, the sub sequent treatment of the separated vapors and liquid being as described hereinbelow.

That portion of the hot gas-oil condensate withdrawn from the fractionator 3 which is not delivered to the absorber I passes through the line I9 and a line I62 to the heat exchanger I56 and thence, if desired, through a cooler I63. The portion of the cooled gas oil is then' delivered through a line I64 to a pump I65 which in turn delivers it in any desired ratio to the quenching lines I30 and I59, for use in quenching the hot cracked products leaving the coils I 23 and I58, respectively. The remaining portion of the cooled gas-oil leaving the heat exchanger I63 passes through the line I64 and through a branch line I66 to a pump IIiI. The pump I6I forces this portion of the cooled gas-oil through a line I68 terminating in two valved branch lines I69 and I10 leading to the lower portion and the upper portion, respectively, of the separating tower 2. Streams of cooled gas-oil may thus be delivered in any desired proportions to the upper and lower sections of the separating tower 2, respectively, as reflux.

The dry gases from the absorber I, comprising largely methane, ethane, ethylene and hydrogen, are removed from the top of the latter through a line I80 having a presssure controlling valve I8I and may be used for fuel gas or otherwise disposed of. Moreover, any portion or all of the dry gases from the absorber 6 may be removed from the system through a line I82 having a valve- I83, instead of passing to the absorber I.

It will be observed that the system described hereinabove provides for the segregation of crude petroleum oil into various fractions, and the presence of normally gaseous hydrocarbons, with little or no oil-recycling, together with recycling of the gas-oil condensate obtained in the various operations to a separate cracking'coil also in the presence of normally gaseous hydrocarbons. In each case, the cracking or conversion treatment is so carried out as to give a higher degree of conversion per pass, or a higher crack per pass, than could be obtained in the same apparatus if the individual oil were cracked in the absence of the normally gaseous hydrocarbons and under temperatures which will ordinarily run from 25 to 300 F. higher than the maximum temperature to which the same oils could be subjected alone without undue deposition of carbon, other factors being the same. All of the gasoline condensate obtained in the system is collected in stabilized form in one point in the system and this gasoline condensate represents a high yield of a product having an exceptionally high anti-knock value when employed as motor fuel.

The process described above in connection with Figs. 1A, 1B and 10 represents onedesirable type of operation which is especially suitable for the treatment of crudes containing a low or medium sulfur content. Where a high-sulfur crude is handled, it may be more advantageous to employ a modified type of operation in order to avoid cor rosion effects.

Thus, in Figs. 2A, 2B and 20 there is shown an apparatus for handling a crude of high-sulfur content, such as West Texas crude.

In the apparatus illustrated in-Figs. 2A, 2B and 2C, the primary apparatus elements consist of a combined crude and viscosity-breaker flash tower 200, furnaces 2M and 202, a vapor-separator and fractionator tower 203, a combined condenser and stabilizer 204, and absorbers 205 and 206. In this instance, the crude is introduced into the system through a line 20'! (Fig. 2B) and is delivered by a pump 208 through a line 209 to a heat exchanger 210, wherein it-is heated to some extent. The

, partially heated crude then passes through line 2| l to a heat exchanger 2i2 wherein it is further heated to a temperature of the order of 500 F. The hot crude is then discharged through a line 2 l3 into an intermediate section 214 of the combined crude and viscosity-breaker flash tower 200. The tower 200 is internally provided with suitable plates or trays 2l5, a trap tray 2l6 and trap-out trays or accumulator sections 2|! and 2l8, the section 2 being located betweenthe trap-out trays 2 i l and 2 l8. In the section 2 I4 the heated crude is distilled at substantially atmospheric pressures by means of hot vapors and its own sensible heat, to remove virgin naphtha and gasoil constituents. The topped crude collecting in accumulator section 2! is withdrawn through a line 2l9 and is delivered by pump 220 through a line 22! to a viscosity-breaker coil 222 located in the furnace 20l and wherein the topped crude is heated under a mild crackingtemperature and under conditions effective to reduce the viscosity of the crude and to produce clean constituents capable off'urther conversion to gasoline under drastic cracking conditions, but notfor the purpose of producing a large amount of gasoline in this operation. In other words, instead of attempting to crack this residual stock to gasoline in one operation, it is thus mildly cracked or viscosity-broken in order to produce a relatively large amount of naphtha and gas-oil constituents suitable for further conversion to gasoline, dirty or residual constituents being separated out. separate cracking of those fractions, in the The temperatures employed in the viscositybreaker coil will vary somewhat in accordance with the nature of the crude and the reaction time employed, but, in general, coil-outlet temsquare inch or higher may be employed. The

hot products from the coil 222 then pass through line 223 having a backpressure valve 224 into the bottom or vapor-separating section 225 of the tower 200 lying below the trap-out tray 2l8. In the section 225 separation of vapors and residual products (tar) is efiected, the tar being removed through line 226 and passing through a tar pump 22! anda heat exchanger 2 l2 to a cooler 228 before being removed from the system through a line 229. tion 225 pass upward through the section 2M, where they mingle with the crude introduced through the line 2|3 and assist in the distillation and fractionation of the crude. oil and lighter constituents then pass through the trap-out tray 2|! into the upper section 230 of the tower 200 and are there subjected to fractional condensation; For this purpose, suitable cooling must be supplied; in the instance shown, a portion of this cooling is supplied by removing a side stream near the top of the section 230 through a line 23L The side stream passes through a cooler 232 and is then delivered by means of a pump 233 to a reflux line 234 back into the top of the section- 230. Additional cool reflux is also supplied to the sections 230, 2 l 4 and 225 through reflux lines 235, 236 and 231, respectively, in such quantities as are required.

A gas-oil condensate, having aboiling range of for example from 400 to 700 F., is withdrawn from the trap-out tray 2ll through a line 238, while a naphtha out, having a boiling range of, for example, from 200 to 500 F., is withdrawn The hot vapors liberated in the sec- .Vapors of gas from the trap 216 through a line 239. Light gasoline vapors and gases uncondensed in the tower 200 are removed therefrom through an overhead line 240 and pass to a condenser 24i and a separator 242. If desired, the light virgin gasoline separated in the separator 242 may be withdrawn from the system through a line 243 having a valve 244, while the gases removed from the separator 242 may be removed from the system, or as in the instance shown, may be removed through a line 245 having a fan or blower 246 which in turn delivers the gases to burners 241 located in the furnace 20L It will be understood that such use of the gases from the separator 242 as a fuel is not necessarily confined to the furnace 20l, as these gases might also be used in the furnace 202 or if available in sufllciently large quantities in both furnaces 20! and 202. p

In any event my invention does not in any sense depend upon the use of these gases as fuel, such use being simply illustrated as a convenient method of utilizing these gases. However, the gasesremoved from the separator 242, in view of the nature of the origin rude charging stock, will contain relatively 1a mounts of hydrogen suitable for recycling to any of the cracking coils because of the resultant high sulfur content which would necessarily obtain in the gasoline produced in any cracking coil to which these gases were delivered. For that reason it is better to remove these gases from the system or to employ them as fuel, whereas other gases produced in the later stages of the operation, or at least fractions thereof consisting primarily of hydrocarbons having 3 to 4 carbon atoms per molecule, are recycled to the various cracking operations as described hereinbelow.

In the operation of the system as described hereinabove, it will be understood that the oil removed through the line 2l9 and delivered to the viscosity-breaker 222 will contain residual crude constituents and heavy constituents obtained from the vapors entering the section 2 from the section 225. The ratio of recycled heavy oil condensate obtained from the vapors to reduced crude will ordinarily be from .5:1 to 2:1.

The naphtha fraction removed through the line 239 passes to a cooler 248 where it is cooled to approximately atmospheric temperature and thence through a line 249 to a pump 250 (Fig. which in turn delivers it through a line 251 to the absorber 205 which receives cracked gases (produced as hereinafter set forth) through a line 252. In the absorber 205, the naphtha fraction acts as an absorption agent to remove from the gases the heavier normally gaseous hydrocarbons contained therein, primarily hydrocarbons having 3 to 4 carbon atoms per molecule. Provision for withdrawing, cooling and returning side streams at a plurality of points in the absorber 205 is illustrated, this apparatus being similar to that provided in connection with the absorber 6 illustrated in Fig. 1C.

The enriched naphtha, containing absorbed normally gaseous hydrocarbons, passes from the bottom of the absorber 205 through a line 253 to an accumulator 254 having a vent line 255 returning to the absorber 205. Enriched naphtha from the accumulator 254 then passes through a line 256 to a pump 251 which delivers it through a line 258 to a heat exchanger 259 (Fig. 2B) and thence through a line 260 to a heating coil 23] located in the furnace 202 (Fig. 2A). In the heating coil 26| the enriched naphtha is subjected to a high cracking temperature in order to crack or reform the same, under conditions efiective to give a higher degree of conversion per pass than would be possible, without carbon stoppage, if the naphtha were heated alone and in the absence of the absorbed normal gaseous hydrocarbons. Suitable coil-outlet temperatures for the coil 26l are from 900 to 1450 F., and coil outlet pressures of 300 to 3000 pounds per square inch may be employed. Typical operating conditions which I have employed in practice are from 1020 to 1030 F. and from 1000 to 1200 pounds per square inch, the liquid volume of the absorbed gases to the volume of naphtha in the furnace charge, measured at atmospheric temperature, being of the order of 1:1.

The hot cracked products leaving the coil 26! are quenched by means of gas oil introduced .through a valve-controlled line 262 and then pass through a line 263 having a valve 264 and thence through a transfer line 265 having a reducing valve 266 into a vapor-separator section 261 located in the bottom of the tower 203.

The virgin gas-oil fraction recovereddfi the trap-out tray 2l1 of the tower 200 (Mg. 2A) is withdrawn therefrom. through the line 238 and passes to a heat exchanger 268 (Fig. 20) where it gives up part of its heat, and thence through a line 269 to a pump 210. A portion of this gasoil is then delivered by means of a pump 2'" to a cooler 212 and thence through a line 213 to the top of the absorber 206 which receives gases containing hydrocarbons having 3 to 4 carbon atoms per molecule, as well as lower-boiling hydrocarbons, through a line 214. In the absorber 206, an absorption of hydrocarbons having 3 to 4 carbon atoms per molecule in. the cooled gas-oil absorption medium takes place. The thereby enriched absorbent passes through a line 215 to an accumulator 216 having a vapor-return line 211 leading back to the absorber 206. The enriched virgin gas-oil then passes through a line 218 to a pump 219 which delivers it through the heat exchanger 268 and a line 280 to a cracking coil 28! located in the furnace Ni, and wherein the enriched gas-oil is subjected to a high crack-- ing temperature under conditions efiective'to produce a higher crack per pass than could be obtained if the gas-oil alone were cracked in the coil 281 in the absence of the absorbed normally gaseous con'stituents recovered in the absorber 206. The coil-outlet temperatures for the coil 28! will run from 900 to 1250 F. and the outlet pressures from 300 to 3000 pounds per square inch, the cracking operation being conducted essentially in the vapor phase. The ratio of liquid volume of absorbed normally gaseous hydrocarbons to the liquid of the gas-oil, measured at atmospheric temperture, will vary from 1:5 to

5: 1, depending somewhat upon the character and quantity of the gases introduced into the absorber 206.

The hot cracked products leaving the coil 28i are quenched by means of cool gas-oil introduced through a line 282 and then pass through a transfer line 283 to the transfer line 265, through which they are introduced into the vapor-separating section 261 of the tower 203 (Fig. 23).

That portion of the virgin gas-oil leaving the heat exchanger 268 and pump 210, which is not employed as an absorbing medium in the absorber 206, is delivered by the pump 210 through a line 284 to the reflux lines 235, 236 and 231 leading into the tower 200 (Fig. 2A), where it is employed as a reflux in the manner stated hereinabove.

Inthe vapor-separator 261 (Fig. 2B) a separation of vapors and residual products or tar occurs, the vapors passing upward to a trap-out tray and accumulator section 290 into a'fractionator section 29l occupying the upper part of the tower 203, while the residual constituents are withdrawn from the bottom of the section 261 through a line 292. preferably recirculated by means of a line 293 to a pump 294, through a cooler 295 and thence back into the section 261, in order to maintain the section 261 free from coke deposition. The remaining portion of the tar withdrawn from the line 292 is either withdrawn from the system or, as shown, is delivered through the line 292 to the section 225 of the tower 200 where it is flashed for the recovery of such vaporizable products as may be retained therein. Any vapors liberated pass into the section 214 while residual constituents are withdrawn as a 2 portion of the tar through line 228.

Suitable provision is made for cooling the fractionator section HI, and this may comprise in part, as shown, the withdrawal of a sidestream through a. line'298, the cooling of this side stream Some of the tar thus withdrawn 18' the return of the cooled side stream by means of a pump299 and a reflux line 299 to the top of the fractionator section 29L Under the influ-' ence of the cooling thus supplied, as well as such additional cooling or refluxing as may be provided for, the cracked vapors rising through the section 29l are fractionated for the recovery .of constituents lying above the desired gasoline boilingpoint range and comprising gas-oil cycle stock. This cycle stock is withdrawn from the trap-out tray 290 through line 300. A portion of this cycle stock is then passed through a line 30l to a hot recycle pump 302, from which it is delivered to a recycling coil 303 located within the furnace 202.

Before being delivered to the coil 303, however, the gas-oil recycle stock is admixed with normally gaseous hydrocarbons containing 3 to 4 carbon atoms per molecule, recovered as hereinafter set forth and introduced into admixture with the cycle stock through a line 304.

In the coil 303 the thereby enriched gas oil cycle stock is subjected to a high cracking temperature under conditions effective to give a higher crack per pass them could be obtained in the absence of the gases. Suitable coil-outlet temperatures for the coil 303 are from 900 to 1250" F. Pressures of 300 to 3000 pounds per square inch are suitable. It will be observed that these conditions are similar to those employed in the coil 28l but the times of contact in the coils RI and 303 may be varied in accordance with the diiferent degrees of refrac- .toriness of the oil stocks charged thereto and also in accordance with the amount and character of the normally gaseous hydrocarbons introduced to the respective coils. In the charging stockintroduced into the coil 303, the liquidvplume of normally gaseous constituents, measured at atmospheric temperature, ordinarily run from 20 per cent to 200 per cent of the liquid volume of the recycled oil.

The hot cracked products leaving the coil 303 are quenched immediately after leaving the. coil by means of gas-oil quenching stock introduced through line 305 and then pass through a transfer line 306 having a reducing valve 301 into the vapor-separator section 261 of the tower 203, thus completing the 'cycle. I

That portion of the gas-oil removed from the tower 203 to the line 300 which is not delivered directly to the ,coil 303 passes'through' the line 308 to heat exchanger or re-boiler 309 where a portion of the sensible heat .of this oil is transierred to the oil in the bottom of the condenserstabilizer 204 and used for the purpose of supplying the heat necessary for stabilization of gasoline distillate. The partially cooled gas oil then passes through a line 310 to the'heat exchanger H0 and a cooler 3 where it is further cooled, leaving the cooler 3 through a line 3l2. A portion of this .cooled gas-oil'may be diverted from the line 3l2 through a line 3l3 having a pump 3H and leading to reflux lines 3l5 and 3H;

which in turn communicate with sections 261 and 29!, respectively, of the tower 203. In this manner the necessary refluxing in the tower 303 over and above that supplied by means of the line, 239, is provided for.

"The remaining'portion of the cooled gas oil passing through the line 3l2 is delivered to a pump 311 (Fig. 2A) which inturn communicates with quenching lines 262, 282 and 305, each of which is provided with asuitable regulating valve. This portion of the gas-oil is thereby divided into three streams for quenching the products leaving the coils 26l, 2! and 303, re-

, spectively.

section 3l9 is withdrawn from an accumulator section ortrap-out tray 320 to a line 32l and passes to a cooler 322 to apump 323 which in turn delivers the cooled condensate through a line 324 into the upper part of the section 319, thereby providing a cooling andrefluxing medium and assisting in the condensation. of the gasoline constituents in the vapors traversing'in the section 3l9. As shown in the drawings, a. portion or all of the light virgin gasoline recovered in the accumulator 242 (Fig. 2A) may also be delivered'by means of a line 325 having a valve 326 and a pump 321, to a reflux line 329 leading into the section 3l9. Wherever the light virgin gasoline is insumcient to supply the desired amount of reflux for the section 3l9 over and above-that supplied through the line 224 or wherever it is desired to segregate the light virgin gasoline from the cracked gasoline and ing upward into 'the section 3|9 while the stabilized gasoline passes through a cooler 333 and thence out of the system through a line 334.

g The pressures\maintained in the towers 203 and 204 will run from 100 to 500 pounds per square inch, and, depending upon the particular pressure employed, the temperature inthe upper part of the tower 204 will run from 60 to 200 F.

The vapors leaving the section 3l9 of the' tower 204 consist of a mixturelof normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule, together with varying quantities of lower-boiling constituents such as ethane, ethylene and methane and, it may be, some hydrogen. These vapors leave the top of the tower 204 through a line 335 and pass to a condenser 330 where they are cooled to approximately atmospheric temperature, thereby resulting in the condensation of a portion of the normally gaseous hydrocarbons contained. therein, primarily butanes and butylenes, together with such small amounts of heavier hydrocarbons as may have escaped condensation inthe section 319. This butane containing condensate is collected in an accumulatorx33l and a portion or all thereof, tiepending upon the amount recovered, is delivered through a'. line 338 to a pump 339 and thence through a line 304 for admixture with the oil about to enter the recycling coil 303, as described hereinabove. The uncondensed vapors and gases leaving the accumulator 331 pass through the line '252 into the absorber 205. That portion of the condensate from accumulator 331 which is not returnedto the coil 303 as aforesaid may also be delivered by means of a. line 340. having a pump 3 into the absorber 205.

In traversing the absorber 205, the gases,'as aforesaid, are scrubbed with cooled naphtha intnoduced through the line 251 and they'are thereby deprived of all or the major portion of the heavier constituents thereof, namely hydrocarbons having from 3 to 4 carbon atoms per molecule. The absorption is so conducted as to move butanes and butylenes as completely as possible.

as well as a portion or all of the propane and propylene. The remaining gases then pass from the absorber 205 through a line 342 having a back-pressure valve 343 and may either be withdrawn from the system througli lines 344 and 345 or may be delivered in part or entirely to the absorber 206 through a line 346 which communicates with the inlet line 214. Hydrocarbon gases from an extraneous source containing hydrocarbon having3 to 4 carbon atoms per molecule are conveniently and advantageously introduced into the absorber 205 through a line 341 which also communicates with the inlet line 214. In traversing the absorber 205 the gases which may comprise residual gases from the absorber 205, or gases from an extraneous source, or both, are scrubbed as aforesaid with cooled gas oil in order to deprive them of their heavier constituents. As in the absorber 205, the operation is so conducted as to remove all butanes and butylenes as well as all or a portion of the propane and propylene.

Q The remainingconstituents, comprising largely ethane, ethylene and methane, then pass through a line 348 having a back-pressure valve 349 into the dry gas main 345, by means of which they are removed from the system.

As in the instance of the absorbers illustrated in Fig. 1C, provision may be made at one or more points in absorbers 205 and 20i-for removing a side stream, cooling it and returningit to the ab-- sorbei', in order to dissipate the heat of absorption and maintain the temperature of the absorbera as low as possible.

The pressure in the absorber 205 will ordinarily run from 100 to 500 pounds per square inch while that in the absorber 200 maybe the same, or somewhat lower, over a range of from 50 to 500 pounds per square inch. These pressures are maintained by means of'the valves 343 and 349, respectively." a g In the system described hereinabove in connection with Figs.- 2A, 2B and 2C. and in which the charge.stock has been described as a crude of high sulfur content, corrosion is limited to the tower 200 and the viscosity-breaker coil 222: the

sulfur compounds in the crude are largely broken up in the coil 222 and leave the tower 200 as hydrogen sulfide in the gases passing to the accumulater 242.

It will be observed that the oils charged to the coils 261 and 28l are virgin stocksin the sense that these stocks have not been subjected to previous conditions as drastic as those employed in .coils 222 and 303. It will be understood that for 433 located in the furnace 401.

gated and only the cracked stock is recycled; therecycling is confined to a single coil and to cracked stock.

The apparatus illustrated in Figs. 3A and 33 may be employed for treating various stocks that are especially suitable for the handling of crude oils containing lubricating oil constituents which it is desired to recover as such. The principal elements in Figs. 3A and 3B are a. crude topping .tower 400, a furnace 40l, a combined vapor-separator and fractionat'or 402, a combined condenser and stabilizer 403 and absorbers 404 and 405. v

In the operation of this apparatus the crude charging stock is introduced through a line 406 to a pump 401 and passes through a line 408 through a heat exchanger 409 and thence through a line 4| into a preheating coil 4! I located within the furnace 40l, wherein the crude oil is heated to a temperature of from 300 to 800 F The specific temperature should be such as to permit subsequent vaporization of gas oil and lighter constituents.

The preheated crude then passes through a line 412 into the crude topping tower 400, which is operated at substantially atmospheric pressure,

and wherein distillation of the preheated crude takes place. The liberated vapors pass upward through the tower and are subjected to fractional condensation, while the crude residuum, containing lubricating-oil constituents, is removed from the bottom of the tower 400 through'a line 4|3A for subsequent working up into lubricating stock or stocks. The necessary cooling in the crude tepping tower 400 is conveniently provided iv withdrawing a side stream through a line 4 l3, cooling this side stream in a cooler 4 Hand returning the cooled side stream by means of a pump 5 to a reflux line 6 to the top of the tower 400.

A virgin gas-oil'cut, having a boiling range of for example from 400 to 700 F., is removed as a side stream through a line 4", while a virgin naphtha out. having a boiling range of for ex:- ample from 200 to 500 F., is removed as a side stream through the line 4l8. The vapors reatmospheric temperature and then passes through a line 426 into the-absorber 404 which receives gases, formed as hereinafter described, through a line 421. The thereby enriched naphtha, containing absorbed hydrocarbons having 3 to 4 carbon atoms'per molecule, then passes through a line 428 to a pump 429 and is delivered through a line 430 to a heat exchanger 431, passing thence through a line 432 to a cracking or reforming coil The conditions maintained in the coil 433 are similar to those described hereinabove in connection with the The 'virgin gas oil fraction recovered in the tower 400 passes through the line 4| 1 to a heat exchanger 431 and thence to a pump 488 which delivers it through a cooler 483 and a-line 490 to the absorber 405, which receives gas through a line 49L In the absorber 405, the cooled gas oil absorbs hydrocarbons having from 3 to 4 carbon atoms per molecule, as in the instances previously described. The thereby enriched gas-oil then passes through a line 492 wherein is located a pump 493 to the heat exchanger 431 and thence through a line 438 to a cracking coil 439 located in the furnace 40L The cracking operation conducted in the coil 439 is similar to that described hereinabove in connection with cracking coil 28! of Fig. 2A.

The hot cracked vapors leaving the coil 439 are quenched by means of cooled gas-oil introduced through a line 440 and then pass through a transfer line 441 and the transfer line 436 into the lower section of the tower402.

In the lower section of the tower 402 a separation of vapors and residual constituents or tar takes place, the tower 402 being similar in construction and operation to the tower 203 of Fig. 2B. Tar is withdrawn through a line 442 and in this instance is removed from the system or delivered to a tar flasher for the recovery of vaporizable constituents.

In the tower 402, condensation of constituents heavier than gasoline is efiected, the condensate comprising a gas-oil or recycle stock. This condensate is withdrawn from a trap-out tray 443 through a line 444, and a portion of the condensate is delivered through line 445 to a pump 446 which in turn delivers it to a recycling coil 441 located within the furnace 40!. Before entering the cracking coil 441 the recycle stock is commingled with liquefied hydrocarbons containg 3 to 4 carbon atoms per molecule introduced through aline 448'. The operation conducted in the coil 441 is similar to that described hereinabove in connection with coil 303 of Fig. 2A.-

tion with the operation illustrated in Figs. 2A,

2B and 2C. Apparatus for these purposes has been illustrated and is similar to that shown in Figs. 2A, 2B and 2C.

The vapors, freed from constituents heavier than gasoline, which emerge from the top of the tower 402, pass through a vapor line 410-to the upper or condensing sectionof the tower 403. In the tower 403, condensation and stabilization of gasoline constituents takes place as in the manner previously described, stabilized gasoline being withdrawn from; the system through a line 41! while the uncondensed vapors pass through a line 412 to a condenser 413 to a separator or accumulator 414. s

A portion or all of the virgin light gasoline recovered in the separator 42| may be delivered by means of a pump 415 to a line 416 to the upper part of the tower 403 as reflux.

The pressure condensate collected in the accumulator 414 is delivered in part or entirely through a line 411 to a pump 418 and thence through a line 448, into the coil 441 as described hereinabove. Any portion of the condensate recovered in the accumulator 414 which is not so delivered to the coil 441 is delivered by means of 1 a pump 419to a line 480 into the absorber 404,

together with gases separated in the accumulator 414 which pass into the absorber 404 through the line 421 The dry gases leaving the absorber 404 through a line 48! may pass through a line 482 and the line 49! into the absorber 405 or they may be removed from the system through lines 483 and 484.

The gases recovered in the distillation of the crude are in this instance delivered to the line 423 to a compressor 424 which in turn delivers them through a line 485 and the line 49I into the absorber 405. Additional gases, from an extraneous source, such as refinery gas or natural gas, containing hydrocarbons having 3 to 4 carbon atoms per molecule, isintroduced where desired through a line 486, passing thence through the lines 485 and 49l to the absorber-405. The stripped gases leaving the absorber 405 pass through a line 481 into the dry gas main 484.

The operation of the various units illustrated in Figs. 3A and 3B, but not specifically described in conjunction therewith, will be readily understood in conjunction with the description accompanying the preceding figuresand particularly Figs. 2A, 2B and 20.

While I have described my invention hereinabove with respect to variousspecific illustrative examples and embodiments, it will be readily understood by those skilled in the art that my invention is not in its broadest aspects limited to the details of such exemplifications or embodiments, but may variously be practiced and embodied within the scope of the claims hereinafter made.

What I claim is:-

1. In aprocess of making low-boiling cracked distillate of high antiknock value when used as a motor fuel, from a crude petroleum, in apparatus of the combination-unit type wherein a crude petroleum is distilled to recover a naphtha fraction and at least one heavier fraction, said naphtha and said heavier fraction are separately cracked, the cracked products are combined for the recovery of tar, cracked gasoline and an intermediate fraction heavier than gasoline, said intermediate fraction is cracked and the thereby cracked products are combined with the abovementioned cracked products for recovery as aforesaid, the improvement which comprises condensing the combined cracked vapors remaining after condensation of cracked gasoline, under pressure, to recover a liquid butane fraction consisting predominantly of hydrocarbons having 3 to 4 carbon atoms per molecule, thereafter scrubbing the gases remaining uncondensed with the aforesaid naphtha fraction, prior to cracking the same, to remove normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule by absorption in said naphtha, cracking the thereby enriched naphtha as aforesaid, and delivering butane condensate, condensed as aforesaid, for admixture with at least one of the other abovementioned fractions about to be cracked as aforesaid.

2. In a process of making low-boiling cracked distillate of high antiknock value when used as a motor fuel from a crude petroleum, in apparatus of the combination unit type wherein a crude petroleum is distilled to recover a naphtha fraction and a reduced crude fraction, said naphtha and said reduced crude fraction are separately cracked, the cracked products are combined for the recovery of tar, cracked gasoline and an intermediate fraction heavier than gasoline, said intermediate fraction is crackedand the thereby cracked products are combined with the above-mentioned cracked products for recovery, as aforesaid, the improvement which comprises condensing the combined cracked vapors remaining after condensation of cracked gasoline, under pressure, to recover a liquid butane fraction consisting predominantly of hydrocarbonshaving 3 to 4 carbon atoms per molecule, thereafter scrubbing the gases remaining uncondensed with the aforesaid naphtha fraction, prior to cracking the same, to remove normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule by absorption in said naphtha,

cracking the thereby enriched naphtha as aforesaid, and delivering butane condensate having 3 to 4 carbon atoms per molecule, condensed as aforesaid, for admixture with said reduced crude fraction about to be cracked as aforesaid.

3. In a process ofmaking low-boiling cracked distillate of high antiknock value when used as a motor fuel from a crude petroleum, in apparatus of the combination unit type wherein a crude petroleum is distilled to recover a naphtha fraction and a heavier fraction, said naphtha and said heavier fraction are separately cracked, the cracked products are combined for the recovery of tar, cracked gasoline and an intermediate fraction heavier than gasoline, said intermediate fraction is cracked and the thereby cracked products are combined with the above-mentioned cracked products for recovery as aforesaid, the improvement which comprises condensing the combined cracked vapors remaining after condensation of cracked gasoline, under pressure, to recover a liquid butane fraction consisting predominantly of hydrocarbons having 3 to 4 carbon atoms per molecule, thereafter scrubbing the gases remaining uncondensed with the aforesaid naphtha fraction, prior to cracking the same, to remove normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule by absorption in said naphtha, cracking the thereby enriched naphtha as aforesaid, and delivering butane condensate, condensed as aforesaid, for admixture with said intermediate fraction about to be cracked as aforesid.

4. The process of making low-boiling cracked distillate of high anti-knock value when used as a motor fuel, from a crude petroleum, which comprises distilling said crude to recover a virgin naphtha fraction and a heavier fraction, passing said heavier fraction in admixture with normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule through an elongated conversion zone of restricted cross-sectional area, under superatmospheric pressure, and there cracking the admixture, delivering the hot cracked products to a vapor-separating zone; removing tar and vapors from said zone, fractionating the vapors to recover gas-oil and gasoline fractions, scrubbing the r maining gases with said naphtha fraction to recover hydrocarbons having 3 to 4 carbon atoms per molecule therefrom, passing the thereby enriched naphtha through an elongated zone of restricted cross-sectional area and there cracking it, and delivering resultant hot cracked products to said vapor-separating zone; the temtions of conversion without such excessive deposition of carbon as to prevent continuous operation of the unit for extended periods of time.

5. The process of making low-boiling cracked distillate of high anti-knock value when used as a motor fuel, from a crude petroleum, which com-' prises distilling said crude to recover a plurality of fractions of different boiling ranges, separately cracking said fractions, combining the hot cracked products and delivering them to a vapor-separating zone, removing tar and vapors from said zone, fractionating the vapors to recover gas-oil. and gasoline fractions and hydrocarbons having 3 to 4 carbon atoms per molecule, cracking said gas-oil and delivering the hot cracked products to said vapor-separating zone, each of said cracking operations being conducted in the presence of returned hydrocarbons having 3 to 4 carbon atoms per molecule in an elongated zone of restricted cross-sectional area under superatmospheric pressure and at a temperature substantially in excess of the maximum temperature to which the respective oil alone and without admixture of said normally gaseous hydrocarbons could be subjected in identical apparatus and under otherwise identical conditions of conversion without such excessive deposition of carbon as to prevent continuous operation of the unit for extended periods of time.

6. The process of making low boiling cracked distillate of high anti-knock value when used as motor fuel from a crude petroleum which comprises fractionally distilling a crude petroleum to recover a naphtha fraction, further reducing the thereby topped crude by contact with hot cracked vapors, cracking the thereby reduced crude in the presence of a liquid butane fraction recovered as set forth hereinbelow, fractionating the resultant cracked products to separate and recover tar, gas-oil, gasoline and liquid butane fractions, scrubbing the remaining gases with said naphtha fraction to remove normally gaseous constituents having 3 to 4 carbon atoms per molecule, reforming the thereby enriched naphtha and combining the hot reformed products with the first-mentioned cracked products for reduction of the topped crude and fractionation as aforesaid, cracking said gas-oil in the presence of normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule and combining the resultant hot cracked products with the firstmentioned cracked products and said reformed products for reduction of the topped crude and fractionation as aforesaid, each of said cracking and reforming operations being carried out under superatmospheric pressure and at a temperature substantially in excess of the maximum temperature to which the respective oil alone and without admixture of said normally gaseous hydrocarbons could be subjected in identical apparatus and under otherwise identical conditions of conversion without such excessive deposition of carbon as to prevent continuous operation of the unit for extended periods of time.

7. The process of making low boiling cracked distillate of high anti-knock value when used as motor fuel from a crude petroleum which comprises fractionally distilling a crude petroleum to recover a virgin naphtha fraction, a virgin gas-oil fraction and a reduced crude, viscositybreaking the reduced crude and commingling resultant vapor with the crude undergoing distillation, cracking the virgin gas-oil fraction in the presenceof normally gaseous hydrocarbons having 3 to 4 carbon atoms per molecule, frac- 

